Air conditioning and refrigeration systems of the type used to cool or keep frozen the loads on large trucks and trailers are conventionally based on closed vapor compression cycles.
One alternative to the closed vapor compression cycle is the use of cryogenic refrigeration systems utilizing either liquid carbon dioxide or liquid nitrogen.
In carbon dioxide-based systems, the carbon dioxide (CO2) is provided in a transportable tank mounted inside the refrigeration unit or on the chassis of the truck. Inside the refrigeration unit, the CO2 is vaporized in an air/CO2 heat exchanger. The cooled air from this heat exchanger is blown into the storage compartment of the vehicle.
Such a system is particularly attractive because, in addition to eliminating the need for chlorofluorocarbons (CFC) or similar refrigerants which can be detrimental to stratospheric ozone, it also eliminates the needs for a refrigerant compressor and the diesel engine or other prime driving unit that drives the compressor.
An example of such a cryogenic refrigeration system that is designed for use with liquid carbon dioxide is described in U.S. Pat. No. 5,730,216.
Another prior art reference, U.S. Pat. No. 5,916,246 describes a system and method for transferring liquid carbon dioxide from a storage tank to a truck transportable tank with lower pressure. The system includes an inlet conduit having a hose portion connected between the storage and transportable tanks for conducting a flow of liquid carbon dioxide therebetween and a vent hose connected to the transportable tank for venting gaseous carbon dioxide.
One disadvantage with the system according to U.S. Pat. No. 5,916,246 for transferring liquid CO2 is that the CO2 loss is relatively high since gaseous carbon dioxide, created as a result of flashing when the pressure of the liquid carbon dioxide is reduced from high pressure in the storage tank to low pressure in the transportable tank, is vented off directly to the atmosphere. Further, as CO2 is introduced into the transportable tank in both a liquid and a gaseous phase, the system will suffer from unwanted long filling periods and difficulties related to flow measurements.
The known filling system is designed to be placed on special truck sites, for instance at or near the garage of the truck owner or warehouse storage and requires a skilled operator to use the system. The known system further requires a skilled person to operate it as the filling operation is not fully automated.
U.S. Pat. No. 4,059,424 discloses an apparatus for the controlled supply of a cryogenic fluid such as argon or nitrogen to a point open to atmospheric air at which it is to be used. The apparatus comprises a storage tank, one phase separator and one liquid container from which liquid phase cryogenic fluid is removed. The liquid phase can be applied by means of nozzles for example in metallurgical applications or by a pouring spout to fill small containers. Depressurization and degasification of the fluid in the separator make it possible for a turbulence-free liquid phase to be obtained in the container.
The present invention is particularly well adapted for transferring a liquid cryogenic refrigerant from a storage tank to a mobile tank, where the liquid is stored in the mobile tank at a pressure above atmospheric pressure. The transfer must be carried out at a pressure well above the atmospheric pressure to reduce losses due to vaporisation of the refrigerant. Another aspect is that if liquid CO2 is depressurized to atmospheric pressure, there will be a conversion of liquid CO2 to CO2-snow or dry ice.
U.S. Pat. No. 6,142,191 relates to an apparatus and a method for metering and transferring LNG-fuel between a storage vessel and a vehicle fuel tank. The LNG is transferred from the storage vessel to a dispenser by means of a motor driven pump. A network of conduits with motor-operated valves and liquid sensors assists in priming the pump so that a vapour-free liquid can be delivered.
This reference does not disclose a method or apparatus for transferring a cryogenic refrigerant between a storage tank and a mobile tank. Further, the apparatus does not include a separator.
U.S. Pat. No. 6,044,647 discloses a transfer system for transferring cryogenic liquid fuel (LNG) between a storage tank and a vehicle fuel tank by heating the LNG to establish a driving pressure that makes pumps or compressors superfluous. LNG is fed by gravity to the pressurizing part of the system. Downstream from this system there is arranged a separator, which allows the liquid phase to be delivered by pressure to the vehicle fuel tank.
This reference relates to combustible liquids and different applications than that of the present invention. Further, heating a refrigerant to obtain a driving pressure for its transferral is not economic as it reduces the cooling/freezing capacity of the refrigerant.
The present invention provides a system for the distribution and sale of cryogenic liquid gases, in particular carbon dioxide that is easily accessible for public use by truck drivers and other users that require quick filling of mobile cryogenic tanks or accumulators.
The system works independently of the level and pressure in the stationary storage tank. The inventive system does not require a transfer pump for transferring the liquid gas from the storage tank to the mobile tank. Therefore, the system is more reliable and maintenance costs are reduced. With the present invention, it is possible to transfer CO2 to the transportable tank while at least some of the CO2 is in a liquid phase, which speeds up the filling procedure.
Further, the measuring of the transferred liquid under filling is simple and reliable. The filling takes place for instance through a quick connector such as a two-port one-piece connector and no manual valves need to be operated by the operator before or after filling which makes the system easy to use. The filling system is accessible by use of a credit card and the user can thereby be invoiced through ordinary credit card systems.
The method according to the invention is characterized in a system of automated filling stations for cryogenic refrigerants, where the filling station for cryogenic refrigerants includes at least a stationary storage tank (1) and a dispenser (3) with at least one refrigerant dispensing means (4, 8) and a quick connector (5) for easy connection to a mobile tank (2) on a truck or the like as defined in the attached claims.
The filling station of the invention includes a pressure/flow control column (30) with a phase separator (20) provided between the stationary storage tank (1) and the dispenser (3), as defined in the attached claims. Preferred embodiments of the invention are also defined in the claims.
The invention will be further described with reference to the attached drawings showing a schematic representation of a system according to the invention.